The prevalence of smart phones enables many people to use various functions of smart phones such as listening to music, watching videos, surfing the web, etc. A smart phone includes a touch screen and provides an unlocking function executed by inputting a password or a pattern. Recently, there has been provided a service that enables a user to unlock the smart phone by knocking or signing on a display through the touch screen.
As a prior art regarding a smart phone providing such an unlocking function, Korean Patent Laid-open Publication No. 2013-0140949 discloses an apparatus and a method for recognizing a user pattern in a device.
Recently, the number of smart devices of each individual person has continuously increased. If a user wants to use multiple devices at the same time, the user needs to unlock each of the multiple devices first.